Snowpack Summary for
Saturday, December 1, 2018 1:59 PMWinter has arrived on the San Francisco Peaks

Overall:
Current new snowfall is 14" at 11,000'. Residual snow from early October has turned to facets at higher elevations on northerly aspects, creating a very weak layer onto which new storm and windblown snow will rest. Other aspects and elevations with no snow cover prior to this storm cycle are barely covered and hazardous to navigate on skis or boards. Avalanche activity may be localized due to wind loading along ridgelines or cross loaded terrain features.

The sequence of two storms this weekend is predicted to deposit 12-24 inches of new snow, with southwest winds loading northwest and east aspects. If precipitation and winds meet or exceed predicted levels, natural avalanches will be possible, and skier triggered avalanches are likely on steep terrain where old snow underlies the new. Stability will deteriorate as the second storm impacts the area Saturday. Size and distribution of avalanches will be highly variable based on the distribution of old faceted snow, and the depth and cohesiveness of the new snow on top.

Starting zones will generally be at and above treeline on cool north facing slopes where storm winds have loaded new snow on top of old facets. Potential avalanche sizes will be dependent on new snow depth and wind re-distribution. Moderate to large avalanches may be possible where faceted snow remains in the starting zones, such as Abineau Canyon and North Core Ridge. Expect early season obstacles and hazards in the thin snowpack...

On lower elevation slopes, baseless new snow will create obstacle hazards rather than avalanche hazards. Early season conditions will exist until more snow arrives and new snow settles and gains density. As the week progresses, changing weather might create a corresponding increase in the avalanche danger, as well as, change the type of avalanche problems you may encounter.

Near and Above Treeline:Expect new and windblown snow sitting on top of old facets. Signs of instability may include "whumphing" and cracking of the snow under your skis or snowboard. If such signs are experienced, stay clear of slopes exceeding 35 degrees and report observations on our website. Early season skiing and riding can be particularly dangerous as overzealous enthusiasm leads to poor decision making.

Below Treeline:Safe backcountry travel may be challenging due to the shallow baseless snowpack at lower elevations. Until the snowpack fills in, hidden logs and rocks are significant hazards. Despite new snow it is still relatively thin out there. North and easterly slopes above 10,000 feet will be your best bet for sufficient coverage to ski/board.

If predicted southwesterly and westerly winds materialize, wind slab avalanches will be possible on high elevation areas on lee facing slopes (NE to E) where slabs may develop on old facets at high elevation.

Looking into the future, with more snow accumulation on tap, instability may remain where snow is loaded on top of old facets at high elevation. Each successive storm may revitalize this instability.

Coverage (remaining from October snow) in Humphrey's Cirque on November 10th, 2018. Photo by Clay Callaway

Final Thoughts

The current storm total of 14" has exceeded all snowfall events of last season...let's hope this trend continues!

Backcountry Permits are required for travel in the Kachina Peaks Wilderness and available at local USFS locations, as well as the Agassiz Lodge on Saturday and Sundays 9 -12 a.m. after the Agassiz Chairlift opens in December.

Weather

Updated Friday November 30th at 1400Our false start of winter in early October was followed by a month and a half of drought. Most of the 12 to 20 inches of snow that blanketed the Peaks above 10,800 feet has disappeared. The exceptions are up high (above 11,000 feet) and on shady north and northwest aspects where shallow snow remains. This snow has reacted to cold, clear conditions progressively turning to poorly bonded facets. Now it appears the pattern may be changing and perhaps winter has finally arrived for real. A significant low pressure system is currently bearing down on us (at the time of publication) bringing anticipated snowfall to the high country above 5500-6000 feet. Snow totals are expected to reach between 12 and 20 inches at 10,800 feet. Storm winds will be out of the southwest and west 29-34 mph, gusting to as high as 49 mph; the perfect velocities for moving snow and loading up leeward aspects. A second storm on Saturday and Sunday will be colder and less moist. Snowline is expected to drop to approximately 4,000 feet adding another 6-12 inches of new snow at high elevations. Cold air will follow the second storm’s exit with gradually warming conditions during the week. A third storm appears to be on the distant horizon. It is too early for any certainty on precise timing of impact, but possibly arriving by the end of next week.

On the afternoon of November 30th, the Inner Basin SNOTEL site Snowslide reported a snow depth of 9 inches (23 cm) at 9,730 feet, and Arizona Snowbowl reported a settled base of 14 inches (36 cm) at 10,800 feet. So far this winter, 23 inches (58 cm) of snow have fallen at the mid-mountain study site. Since November 23rd, SNOTEL temperatures have ranged between 47° F on November 27 and 15° F on November 25th. For the same period, the AZ Snowbowl Top Patrol Station (ASBTP, 11,555 feet) the temperature ranged between 38° F on November 27 and 15° F on November 23rd.

Avalanche Problems/Characters

The avalanche problem/character describes part of the current avalanche danger. However because we only realease a summary once a week, the current avalanche problem will likely change.
Understanding avalanche problems is essential, because it allows you to determine your approach and strategies to risk treatment. Below are brief descriptions of avalanche problems/characters, and links to detailed information on the problem, formation, patterns, recognition, and avoidance strategies.
Avalanche Problems Explained Also see the North American Danger Scale.

Loose Dry

Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose-dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose-dry avalanches can trigger slab avalanches that break into deeper snow layers.

Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
more info

Storm Slab

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
more info

Wind Slab

Release of a cohesive layer of snow (a slab) formed by the wind.
Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side.
Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard.
Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features.
They can be avoided by sticking to sheltered or wind-scoured areas.
more info

Persistent Slab

Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow.
Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices.
They can be triggered by light loads and weeks after the last storm.
The slabs often propagate in surprising and unpredictable ways.
This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
more info

Deep Persistent Slab

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground.
The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
They commonly develop when Persistent Slabs become more deeply buried over time.

Deep Persistent Slabs are destructive and deadly events that can take months to stabilize.
You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.
more info

Loose Wet

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers.
Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
more info

Wet Slab

Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very destructive.

Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty.
more info

Cornice Fall

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side.
Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridge line areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
more info

Glide

Release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

Predicting the release of Glide Avalanches is very challenging. Because Glide Avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide Avalanches.
more info

Snowpack Summary Disclaimer

The summaries on this site were written by Kachina Peaks Avalanche Center Board Members. They are based on a broad spectrum of data collected from weather stations, National Weather Service point forecasts and field observation by qualified individuals.

These summaries are factual information based on past and current conditions and are not forecasts of what will be encountered in the future or a declaration of the current avalanche danger.

The summaries are not intended to substitute for good knowledge and decision making skills in avalanche terrain. If you have any doubt of stable conditions, please stay away from avalanche terrain. You can usually find good places to go that are not prone to avalanches, such as on low angle slopes away from avalanche run-out zones. If you have any questions about where to find such places, you should consider further avalanche educational opportunities, such as those listed on our education page.

Snowpack Summary – Format and Limitations Statement

Starting in 2012 Kachina Peaks Avalanche Center (KPAC) has publish a weekly Snowpack Summary on our website.
These summaries are currently issued on Friday afternoons. On occasion, we will give storm updates or warnings of rapidly increasing avalanche hazard at more frequent intervals.
Our objective is to reach weekend recreationist, informing this user group of prevailing conditions, but particularly warning of avalanche hazards whenever they are present.
Many people have asked us why we use the format we do, but do not include a danger rating or a hazard/stability rose as many other avalanche centers do around the west.

The National Avalanche Center (NAC) advises small operations like KPAC, who do not issue daily bulletins to not use danger ratings in our snowpack summaries due to the regular but intermittent nature of their field observations and the length of time between issuance of snowpack summaries.
A primary concern is for how conditions can change in the time between publications, potentially giving the public misleading information. At this point, we simply do not have resources to monitor the snowpack at the level necessary to accurately produce more frequent bulletins.
While we understand the benefits of a danger rating using the North American Danger Scale, we also feel that our format encourages people to dig in a little deeper, and spend some time reading what our forecasters are saying. Although the area that we forecast is relatively small, the variability has proven quite large.
Inner Basin conditions are often surprisingly different from those on the more wind-affected western side on the Peaks.

We hope the information that we provide in summaries helps give you a good overview of what is going on out there, and what avalanche problems you should be attentive to, but if there is every uncertainty, then we encourage you to ask questions via Facebook or our Observation/Discussion Boards.